Add one more subtest to global_func15 selftest to validate that
verifier properly marks r0 as precise and avoids erroneous state pruning
of the branch that has return value outside of expected [0, 1] value.
Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
---
.../selftests/bpf/progs/test_global_func15.c | 32 +++++++++++++++++++
1 file changed, 32 insertions(+)
diff --git a/tools/testing/selftests/bpf/progs/test_global_func15.c b/tools/testing/selftests/bpf/progs/test_global_func15.c
index f80207480e8a..d81781eba1b6 100644
--- a/tools/testing/selftests/bpf/progs/test_global_func15.c
+++ b/tools/testing/selftests/bpf/progs/test_global_func15.c
@@ -22,3 +22,35 @@ int global_func15(struct __sk_buff *skb)
return v;
}
+
+SEC("cgroup_skb/ingress")
+__log_level(2) __flag(BPF_F_TEST_STATE_FREQ)
+__failure
+/* check that fallthrough code path marks r0 as precise */
+__msg("mark_precise: frame0: regs=r0 stack= before 2: (b7) r0 = 1")
+/* check that branch code path marks r0 as precise */
+__msg("mark_precise: frame0: regs=r0 stack= before 0: (85) call bpf_get_prandom_u32#7")
+__msg("At program exit the register R0 has ")
+__naked int global_func15_tricky_pruning(void)
+{
+ asm volatile (
+ "call %[bpf_get_prandom_u32];"
+ "if r0 > 1000 goto 1f;"
+ "r0 = 1;"
+ "1:"
+ "goto +0;" /* checkpoint */
+ /* cgroup_skb/ingress program is expected to return [0, 1]
+ * values, so branch above makes sure that in a fallthrough
+ * case we have a valid 1 stored in R0 register, but in
+ * a branch case we assign some random value to R0. So if
+ * there is something wrong with precision tracking for R0 at
+ * program exit, we might erronenously prune branch case,
+ * because R0 in fallthrough case is imprecise (and thus any
+ * value is valid from POV of verifier is_state_equal() logic)
+ */
+ "exit;"
+ :
+ : __imm(bpf_get_prandom_u32)
+ : __clobber_common
+ );
+}
--
2.34.1
